1. Field of the Invention
The present invention relates to a procedure and to an apparatus for the deceleration of an elevator.
2. Description of the Related Art
According to various elevator regulations, an elevator must be able to stop at a landing with a certain accuracy. The required tolerance is typically of the order of .+-.5 mm, which is easily attained by modern elevators. However, a greater stopping precision is aimed at, because the stopping accuracy is also regarded as a measure of quality of the elevator. Moreover, the co-operation between certain parts of the elevator equipment, such as the car door and the landing door, is better in an elevator capable of accurate stopping.
The determination of elevator position is implemented using pulse tachometers mounted in conjunction with the machinery and giving pulse counts that are directly proportional to the revolutions performed by the machine. Another device used for the determination of elevator position is a tachometer which produces an analog voltage proportional to the elevator speed and whose output voltage is converted into a pulse train in which the pulse frequency is proportional to the speed and the pulse count to the distance covered by the elevator. However, in both tachometer types, the distance calculated from the pulse count is not quite accurate because the elevator is driven by means of the friction between the elevator ropes and the traction sheave. The distance calculated from the tachometer pulses contains a small error, because there occurs a slight movement of the elevator ropes relative to the traction sheave. Although the error in the calculated distance is not large, usually only a few millimeters, an objective in modern elevator technology is to eliminate even this small error.
Various solutions have been proposed to solve this problem, e.g. by updating the pulse counts representing elevator position at each floor, as is done in U.S. Pat. No. 4,493,399. In some elevators two tachometers, an analog tachometer and a pulse tachometer, are used, together or separately. Another solution used to indicate elevator position is to provide the shaft or car with code reading devices producing accurate position data.
The behavior of an elevator is also controlled by factors relating to passenger comfort, such as e.g. acceleration, deceleration and changes in them, which, though in fact irrelevant to the problem of determining elevator position, impose certain edge conditions regarding elevator control.